This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Duchenne muscular dystrophy (DMD), the most prevalent fatal genetic muscle disorder of children, is caused by mutations in the gene for the protein dystrophin. One caveat for dystrophin replacement therapy in these patients is the likelihood of the immune system seeing the introduced protein as foreign. Utrophin, a protein very similar to dystrophin in structure and function is normally expressed throughout the human body. During development utrophin expression can be found at the muscle membrane. However, shortly after birth there is a replacement of utrophin with dystrophin. Targeted delivery of utrophin may provide a therapeutic benefit in DMD patients, particuarly those with large deletions in the DMD gene. We have designed and delivered a murine microutrophin cassette via AAV/6 which drastically reduced key indices of muscle disease in mice that lack both dystrophin and utrophin (mdx/utrn-/-), similar to microdystrophin. Over the past year we have continued to investigate the use of utrophin as a potential therapy by evaluating in the context of our presently most active muscle specific regulatory cassette (CK8) in mdx and mdx/utrn null mice. We have also delivered this same cassette in the non-human primate (NHP) model intramuscularly comparing relative expression level to the CMV promoter. Likewise we have evaluated the immune response by measuring antibody titers and T-cell responsiveness to AAV6 capsid and microutrophin peptide panels. Future efforts are aimed to refine our large animal delivery approaches, and to further characterize the immune response against administered vector in the NHP model in the context of our delivery methodologies. The findings from the proposed studies will provide critical data regarding biodistribution, dosing, and toxicity within the NHP thereby enhancing translational research for gene therapy of DMD patients.